The weight does take some getting used to. It's very light and slick. I don't have a case as the selection is currently pretty sucky. While I'm tempted to go commando, I think I might still go the bumper route for some mild protection like I had on my 4S. I'm tempted to go the AppleCare+ route where they'll replace it for $49 if there's physical damage, but a broken phone is a hassle, even if they overnight it. Still trying to decide. Such important and difficult decisions...

I've been going sans case and have liked it. Without a glass back like the 4S, I don't have to obsess constantly about fingerprints, so that's an improvement.

I did buy an Incipio "Feather" case, which adds almost no weight/bulk, but I haven't really used it.